How long will chloroform knock a person out for?

Chloroform is basically an anesthetic--but one that is no longer used due to the fact that it can seriously damage your liver and heart. Even with perfect dosing, it would take at least 5 minutes of breathing it to knock someone unconscious.

Is it illegal to have chloroform?

Although synthesizing chloroform requires the sophisticated knowledge of a chemist, there is no permit necessary to purchase it, and the substance can be readily purchased at most chemical-supply stores. But remember: Just because you can get your hands on it, doesn't mean you can use it like they do in the movies.